Catheters have been in common use in medical practice for many years. They are often used, for example, to probe locations inside a body or a patient which are otherwise unreachable without surgery. A catheter is first inserted into a vein, artery, or other structure or region of the body of the patient. The catheter is then guided to the area of concern by further inserting it into the patient's body. As medical knowledge increases, more uses of catheters have been developed and these uses have become more complex so that the ability to accurately and selectively steer the distal portion of the catheter has become of extreme importance. For example, there is a need to use steerable catheters to supply or remove fluids or cells to or from various internal tissues of the patient and to apply or sense electrical signals to or from such tissues. Administered fluids may, for example, be in the form of a liquid, suspension or gel containing a drug or other chemical used, for example, to treat or anesthetize the tissue.
In order to place the tip of the catheter in the correct location and position, it is often necessary or highly desirable to variously curve the catheter so that its distal portion will travel into the proper anatomical region as the catheter is inserted into the patient. After the distal portion has been so curved, it is also often desirable to rotate the catheter while maintaining the curvature of the distal region so that the intended portion of the catheter can then approach and/or contact the particular tissue of interest. It is also important that the catheter be able to make firm contact with the tissue of interest to facilitate reliable application or removal of fluid by the catheter and/or reliable transmission or sensing of an electrical current to or from the tissue.
A catheter which addresses some of the above problems is disclosed in U.S. Pat. No. 5,190,050, the entire disclosure of which is expressly incorporated by reference herein. In the catheter disclosed therein, the distal portion easily and reliably bends or twists in an angular orientation or curve that is selectively controllable. The distal end of the catheter is hollow and has at least two flat planar rigid juxtaposed shims mounted therein. The distal ends of the shims are attached to one another while the proximal end of at least one of the shims is attached to a pull cable and ultimately to the catheter handle. When a doctor or other user manipulates the catheter handle so that the catheter translates distally with respect to the handle, one of the shims follows the distal translation while the other shim retains its longitudinal distance from the handle causing the other shim and the associated distal portion of the catheter to longitudinally bend. Because of the planar shape of the shims and their rigidity, the bending of the distal portion of the catheter is always identical in direction, although varying in degree proportionally to the magnitude of the manipulation of the catheter handle, and is in a single plane of movement. The distal portion of the catheter can also optionally carry contact electrodes to transmit electrical pulses to or from tissue of the patient's body or can be made to pump fluids into or out of the body of the patient.
Although the catheter disclosed in U.S. Pat. No. 5,190,050 is reliable, completely functional and useful for many applications, the location of the shims and associated support structure between the shims and catheter handle within the hollow distal portion of the catheter results in contact between fluid flowing through the catheter and the shims and associated support structure. Depending on the construction material of the shims and support structure, and the properties of the fluid, such contact might in some cases introduce impurities into the fluid. This would be undesirable if fluid is being extracted from the patient through the catheter for laboratory testing, or if fluids are being delivered to the patient through the catheter such, for example, as medication, or liquids, suspensions, gels or gases containing a drug or other chemicals as may be used to treat or anesthetize the tissue. Additionally, such fluids could perhaps damage the shims and associated support structure, as by corrosion or clogging.
There are certain internal passages or chambers in the body which are not easily accessible to a catheter that can bend in only one plane. In the heart, for example, when it is desired to apply electrical pulses to or to introduce or extract fluids to or from the mitral or tricuspid valve annulus the tip of a catheter must be curved in two planes in order to properly contact the desired tissue. When the steerable catheter disclosed in U.S. Pat. No. 5,190,050 is used for this particular application, a doctor typically introduces the tip of the catheter into the heart's atrium and adjusts the catheter's handle to cause the tip to deflect in its single plane of deflection. The distal portion of the catheter's tip is then manipulated, either by rotation, by further insertion, or by a combination of both so that it contacts and is wedged against certain tissues and/or tissue walls within the heart. As a result, a proximal portion of the tip of the catheter, which does not contain the sandwiched juxtaposed rigid shims, is caused through such contact or abutment with tissue walls to assume a curve or bend in a plane that is different from the deflection plane of the distal end of the catheter's tip. As a result of this double twist in the catheter's tip, the catheter can then be further inserted so that it enters the mitral or tricuspid valve annulus. The second twist in the tip of the catheter, however, is not fixed or locked, is not readily controllable or selectively attainable, and is not pre-programmed into the catheter. As a consequence, the catheter tip manipulations needed to attain the desired catheter tip shape require substantial experience and skill.
The bi-directional steerable catheter disclosed in U.S. patent application Ser. No. 08/259,390, filed Jun. 14, 1994, the entire disclosure of which is expressly incorporated by reference herein, employs a single planar shim, the distal end of which is attached to two pull cables, one disposed on each side of the shim. When one pull cable is pulled, the other is correspondingly loosened, thereby causing the tip of the catheter to bend. The movement and curvature of the catheter's tip is selectively controlled by a user's manipulation of the catheter's handle. This catheter can thus bend in two directions in a single plane. The multiform twistable tip deflectable catheter disclosed in U.S. Pat. No. 5,358,479, the entire disclosure of which is expressly incorporated by reference herein, employs a single shim with at least one transverse or lateral twist which enables the tip of the catheter tube to assume a lockable pre-programmed curvature in more than one plane. Although the catheters disclosed in U.S. patent application Ser. No. 08/259,390 and in U.S. Pat. No. 5,358,479 are also reliable, completely functional and useful for many applications, if a fluid is to be transported through the catheter, chemical reactions between the fluid and the catheter's internal elements may occur which may reduce the effectiveness of the catheters or affect the purity of the fluids being transported through the catheter.